The importance of the pigment epithelium in the visual process has long been appreciated and recently there has been renewed interest in elucidating some of the fundamental biochemical and physiological characteristics of these cells. The present study will be carried out on isolated pigment epithelial cells from cattle eyes; special care will be taken to prepare the cells free of contaminating materials, especially rod outer segments. They will then be fractionated by differential centrifugation and the individual fractions purified fuuther by the use of density gradients. The intracellular distribution of various enzymes will be determined with special emphasis being placed on these concerned with the degradation of macromolecules. Phagosomes will be isolated in as pure a state as possible and their chemical and enzymatic properties investigated. The intracellular distribution of vitamin A, both free and esterified, will be examined. It is anticipated that the information derived from these studies may shed some light on the pathogenesis of certain retinal diseases, inter alia, macular degenerations, and retinitis pigmentosa and other inherited disorders affecting the retinal pigment epithelium.